Measuring instrument



Nov. 10, 1942. c. L BRADFORD Erm. 2,301,193'

/ MEASURING INSTRUMENT A Filled May l0, 1940 l LocK FREE y 74 W7? ATTORNEY\Y Patented Nw. 10,1942

Colin Irving Bradford, Stratford, and Paul E. Lowe, Bridgeport, Conn., assignors to Remington Arms Company, Inc., a corporation of Delaware Application May 10, 1940,l Serial No. 334,300

(Ci. ll-l) 5 Claims.

This invention relates to an apparatus for `measuring time intervals and particularly intervals that are extremely short, using a ballistic galvanometer or other instantaneous charge .measuring device as the indicating instrument. Accurate measurement of short time intervals is desired and necessary in many precision devices. As an example, the measurement of the iiight of afprojectile through a barrel or externally of the barrel occupies a very short space of time.

' Accurate measurements of time intervals are also necessary in devices, such as instruments used for sounding purposes to determine the depth of the ocean.

As.still further examples of the miscellaneous applications may be mentioned the measurement of the time ci.' operation oi relays, circuit breakers, sound locaters, and many other operations involving short time intervals from which an electrical limpulse can be obtained at the beginning and end ci the interval.

The basic requirements of any measuring instrument, are accuracy, ease of operation, portability and other related merits. For velocities over short ranges and for barrel time with times f between 0.002 and 0.040 second, the accuracy of the conventional Boulenge chronograph, for example, is not all that is desired. This invention has as one of its objects the development ci an accurate instrument for measuring short time intervals and to provide a chronoscope which is portable, direct reading and adaptable to the accurate 'measurements oi time intervals. Another object of this invention is to provide an indicat- 'ing device which may be readily calibrated so as to be direct reading. The deflection of the ballistic galvanometer in this invention bears a direct relation to time. The invention contained herein constitutes an improvement over the invention disclosed in application Serial No. 276,167, led May 2'?, 1939. From the following illustrative description, in which are disclosed certain embodiments of the invention, as well as details and means for carrying itl out, it will become apparent how the foregoing and other objects may be accomplished. y

In the drawing:

Fig. 1 is a schematic drawing of a ballistic I range, which shows several devices for indicating the time at which a projectile is at particular points of its flight.

Fig. 2 is a simplified circuit arrangement, showing one way in which the invention may be carrled out.

Fig. 3 is a circuit arrangement embodying the invention of the circuit of Fig. 2, and having means to determine the constants of the galvanometer, and also including a protective circuit.

Essentially, the chronoscope disclosed herein consists of two gaseous discharge tubes which are normally non-conducting, with a ballistic galvanometer in the plate-cathode circuit oi one of the tubes. A suitable impulse is used to change the potential of the control electrode oi the rst tube, which renders the tube conducting and causes a ow of current through the ballistic galvanometer which is in its plate-cathode circuit. A suitable impulse at the end of the interval to be measured is used to change the potential upon the grid of the second tube, causing it to become conducting. As a result of the flow of current through the plate cathode circuit oi the second tube from a source of energy, such as a battery therein, the plate potential ci the first Itube is so depressed relative to the cathode thereof as to cause the first tube to become non-conducting, thereby stopping the flow of current through the ballistic galvanometer.

Referring to Fig. l, there is shown, merely by way of example, one manner of using the invention wherein 2d indicates the walls and roof o a ballistic range. In the firing chamber, there may be located a breech mechanism 2l which may be fastened in any suitable manner to a iirm foundation. At the other end of the range there is located a target plate 25, against which a projectile fired from the barrel may be directed. There may be a disjunctor contact 30 of conventional design located back oi the target plate. There may also be provided some suitable means at the muzzle of the gun or responsive to the fall of the hammer upon the primer of the projectile to provide a suitable impulse to indicate the starting or the projectile in its ilight. The bullet striking target plate 25 will cause the contact 3B mounted on the pendulum to be moved away from the plate 25, thereby breaking contact and causing an impulse oi some description. The details oi the ballistic range are well-known and are not a part oi this invention. It is evident that many various forms and devices may be Q passing through the instalment, the equation being zkQ wherein k indicates the instruments constants.

T that the current ows. the equation Q=IT will express the relation existent, and that the galvanometer deilection will be :EIT

The time interval can then be determined, if k and I are known, because tons, although not limited to the precise form shown. In such a gaseous or vapor tube, the grid or control electrode, as it becomes more positive, will finally reach the critical point where the tube will become conducting. The control grid then loses control of the to stop the tube in its conduction. In order for the tube to remain conducting, it is necessary that the platebe kept above a certain potential. When a plate isdepressed relative to a cathode below this potential, the tube will become nonconducting. The closing of the circuit 3i and The constant k can be readily determined, be-

cause if a condenser oi capacity Cc is charged to a potential V, the charge willequal CcY, or

Then if the condenser be discharged through the galvanometer and the deflection D observed. it will follow that The circuits for determining the constant 1c will be set forth at a later point. The current I can be determined by a steady state measurement, using a resistance that is the equivalent of the galvanometer resistance. Then, since 6 Ttr and then By letting CLV lars and in this way the range of the instrument may be varied over wide limits.

Operation Fig, 2 shows a. simplified circuit which may be utilized to practice the invention disclosed herein. The circuit of Fig. 2 is shown without the means for producing the impulse received at the beginning of the initial time interval, and such will b discussed at a later point. It is suihcient that the input terminals 3| and 32 are connected to a switch which may be closed in the example shown, to produce the desired impulse upon the ilrst gaseous discharge tube, It is to be understood that the discharge tubes may be of the gasecus or vapor type, sometimes known as 'thyra- 7s 32 causes a current to flow from the battery 33 to one side of condenser 34 and through resistance 35 back to the battery. This will cause the grid 3l to change its potential and become more positive, thereby causing tube 31 to become com ducting. A ballistic galvanometer 38 is located in the circuit, including the plate 38, cathode 40, battery 4| and resistance 42, current will flow through the nometer for a given time. It has been shown that the galvanometer will measure the quantity flowing therethrough, which will be the amount ilowing from the time tube 31 becomes conducting to the time at the end of the interval when it becomes again non-conducting. A second impulse received atvterminals 43 and 44 will simitube and galvallarly ail'ect the grid 45 of gaseous discharge tube 46, and establish a flow oi.' current from battery 41 to plate 48, cathode 49, through battery 4I, resistance 42, and back to battery 41. In the manner about to be described, this flow of current which occurs when tube 46 becomes conducting, will depress the plate potential on plate 38 of tube 31 so as to render the tube 31 nonconducting. The anode, or plate voltage on tube 31 may be expressed. by the equation Emilia-1R42, 1R42 ybeing the potential drop across resistance 42. The anode voltageon tube 31 during extinction at the moment the tube 46 becomes conducting, allowing thedischarge oi' battery 41 therethrough is E271: (Eri-1R42) -InRu where In is the current of battery 41, which also passes through resistance 42. Previous to this, tube 31 remained conducting because the potential drop across resistance 42 with the current from battery 4| was not sulcient to depress the plate potential to the point where tube 31 would become non-conducting. However, the ad ditional ow of current through 42, caused by the ow oi' current from battery 41, will lower the plate potential 39 below the critical value necessary for the tube to remain conducting. This may be expressed as Es'rzr-Es'lc-IMRQ the term Irv/R4: being a potential which depresses the anode of the tube 31 to such a point as to be below the critica.' value and cause the tube to become non-conducting. It is seen, therefore, that as the current has stopped ilowing through the galvanometer 38, that the quantity which has passed he'ethrough will give a direct reading oi' the interval between the time that tube 31 became conducting and tube 46 became conducting.

It is also to be understood that the tubes shown are for illustration only, and that multigrid or other element tubes may be used.

By the invention described herein, the switch l which is responsive to the beginning or end ol.'

the time interval to be close the input circuits.

Referring particularly to Fig. 3, 50 and li may t measured mary 017er! 0I tube and will not serve so that a steady lllig. 2. A condenser 52, Aresistance 53 and battery-54 are provided, which are similar to con denser 54, resistance 55 and battery 35 of Fig. 2. The charging of condenser 52 from battery 5t will serve to apply a positive potential to grid 55 of tube 55. AResistance 51, switch 55, and battery 55 are connected across the input terminals. If it is desired to use a switch or device that clos at the beginning of the interval to be measured, the switch 55 is left in its open posil tion, as shown in Fig. 3. 'Ihe circuit will then be closed from battery 54, terminal 55 through the switch (not shown), terminal 5l, condenser 52,

resistance 53, back to battery 54. This will apply a positive potential to grid 55.- If it is desired to use a switch between 55 and 5| that opens upon the change of condition at the beginning of the interval to be measured, the switch sa is closes and, when the impulse responsive switch is opened, the potential of battery 55 will appear upon the plate o! condenser 52, the flow being from battery 5l, switch 55, resistance 51, condenser 52, resistance 53, battery 54, line`55, and backto battery 55. It is seen, therefore, that either the opening or closing of a switch, responsive to the beginning of an interval, connecting input terminals 55 and 5i together will cause a positive potential or change in potential upon the grid 55, sufiicient to render the gaseous discharge tube 55 conducting. lA leak-oi! 5I ot high resistance may be connected across the plates of condenser 52, which will allow the charge thereon to slowly leak of! so that the circuit will be in readiness for the next impulse to Ibe received at the next operation. A similar arrangement may be employed for the input terminals 52 and 55 for the impulse to be received as a result of a change in condition at the end of the interval to be measured.

vThe circuit shown in Fig. 3 essentially convains the circuit of Fig. 2 with a few changes, and, in addition, has means'ior Calibrating the galvanometer and for determining its constants and a protective circuit to operate the second tube in the event that a second impulse is not received. A galvanometer 54 corresponding to 55 of Fig. 2 is located in the plate-cathode circuit of tube 55 instead of being directLv in the connection between the plates of the two tubes.

The galvanometer 54 is located between the cathode 55 and the negative side of battery 55. Battery 55 corresponds to battery 4I of Flg.`2. A switch operating handle 51 of conventional type,

which is pivoted at 55, may be employed to reciprocate the operating bar 55. It is to be understood that the switch shown in Fig. 3 is diagrammatic in form and may take any of a different number of forms. For the purpose of illustration, the bar 55 has the projections 15 thereon for the purpose of operating the switch levers 1I, 12, 13 and 14 in a manner which will be described presently. When it is desired to take a reading with the instrument, the switch operator 51 is moved to the right in the direction indicated by'arrow 15, which moves the operating bar 55 to the left. The springs H4, H5,

H5, H1 are employed to urge the switch levers 1l, 12, 13, 14 in the direction oi said springs. After the reading has been taken, the removalof pressure upon operator 51 will allow the switch to return to the neutral position shown in Fig. 3: Ii it is desired to calibrate the instrument, the

. switch isvmoved in the direction shown by arrow I5 where'it may be locked so that the proper readings may be taken. A resistance 11 which is the equivalent oi the resistance of the galvanometer 54 may be provided. A condenser 18 vanometer 54 is also provided. The battery 19.

is placed in the plate cathode circuit of the second gaseous discharge tube 50 and is similar to the battery 41 of Fig. 2. The resistance 8l corresponds to the resistance 42 of Fig. 2. Resistance 8l may be variable so that the range ot the instrument can be changed.

A description will first be given of the setting of the apparatus for the taking of a reading, following which a description of the calibration circuits and protective circuits will be given. In order to takea reading, the switch operator 51 is moved in the direction indicated by 15, which will move the operating bar 59 to the left and close switch lever 12 upon contact 82, switch lever 13 upon contact 83, and switch lever 14 upon contact ad. When in this position, an impulse placing a positive potential upon condenser 52 in a manner which has previously been described will cause gaseous discharge tube 56 to become conducting. A current will then iiow in the plate cathode circuit of said tube from" cathode 55, line 85, contact 82, switch blade 12, line 88, galvanometer 54, milllammeter 81, line 58, line 85, to the negative side of battery 55, line 95, through variable resistance 8l, line 9i, line 92, back to the plate 93 or tube 55. This is similar to the plate-cathode circuit of tube 31 (Fig. 2) with the exception that the galvanometer is en the opposite side oi' the resistance 42 and battery 4i. The ballistic galvanometer will de- 52 and 55, indicating the end of the interval to be measured, places a positive charge upon condenser 52' and changes the potential of the grid 54 of tube Si?. Tube 8c will thereupon become conducting and Athe plate-cathode circuit thereof may be traced from cathode 95, line 89, negative side oi batte. 55, line et, resistance 5i, line 9|, line 95, contact 84, switch'lever 14, battery 19, back to the plate 91 of tube 89. The additional current from the plate-cathode circuit of tube through resistance 8| will cause a drop in the potential of the plate side of tube 55, such that the plate potential of tube 55 will fall below the critical value necessary for this tube to remain conducting, and tube 55 will thereupon be'- come non-conducting, interrupting the now of current through galvanometer 54. Thus it is seen that the tube 55, upon becoming conducting, will start a iiow through galvanometer 54 which will be stopped upon an impulse being received by tube 80, which starts tube 85 to become conducting. After 'thisreading has been made, if the operator releases the switch 51, the switch will return to the neutral position and will break the circuit between contact 84 and switch lever le, thereby breaking the plate-cathode circuit of tube 8l! so that the tube will again become non-conducting. It is evident that when the impulse is received by the second tube 8B that it will extinguish the rst tube 55, which will then remain extinguished until the platecathode circuit o the second tube is broken by the switch Bl returning to neutral position. In this manner, a second impulse or impulse due to cludes means to impress an impulse upon the grid l.

oi' tube 80 after a given period of time ln the event that an impulse is not received at terminals 62 and 63. A variable resistance, such as that shown at 98, may be employed so that the device may be set for any given desired interval, this being necessary so that the interval may be adjusted, so that the second tube will not be shut on? before the end of the interval to be measured, and that theprotective circuit will only operate after a given settime thereafter. A Vdead point or terminal 99 is provided for the resistance adjusting means, so that the calibration operationsma'y be made without the protective circuit operating to interfere. At the time that the ilrst tube 56 becomes conducting, the proteotive condenser |00 is charged from point |0| through one of the resistances 98. A discharge device |02 is connected in series with the secondary |03 o1' a protective transformer |04, the de vice |02 and secondary |03 being parallel to the protective condenser |00. The discharge device |02 may be of any suitable type, such as a neon tube wherein a potential of sufficient value will render the tube conducting or cause the device to become conducting. It is seen that as the current flows through resistance 8| as the tube 56 becomes conducting, that protective condenser |00- will be charged. When the charge reaches a certain value, the discharge device |02 will break down, allowing an impulse to flow through the secondary of the transformer |04, which will place an impulse upon the grid 94 of tube 80. This will have the same effect on the tube 56 as though an impulse has been received at input terminals 62 and 63 and will shut oil the tube 56, thereby preventing the device from operating after a given interval even though no impulse has been received at terminals 62 and 63.

The means for Calibrating the instrument will now be described. Switch operator 61 is moved in thedirection indicated by arrows 16, wherefrom the plate of condenser through switch lever 13, contact |01, to the side of battery 66, line 89, line 88, milliammeter 81, switch lever ||0, back to the plate of condenser 18. Then the condenser 18 may be discharged through the galvanometer 64 by moving switch 61 to the right so that contact will be made by the switch lever 13 and point 83. When this is done, current will flow from the -lside of condenser 18, through switch lever 13, point 83, line 86, galvanometer 64, switch H0, back to the side of condenser 18. The voltage or potential of battery 66 may be determined by closing switch ||2 to resistance ||3 whereupon the circuit may be traced as follows: -1- side of battery 66, resistance |l3, line |09, milliammeter 81, line 88, line 89, back to battery 68. The resistance ||3 is of such a value as to cause 81 to function as a voltmeter. From these readings, constants of the galvanometer can be determined because the capacity of condenser 18 is known and deflection D has been observed. All this has been set out in detail in application Serial No. 276,167.

'It is seen that in the improvement of this invention that a source of energy, such as a battery, has been substituted for a source of energy, such as a condenser, to be used to depress the plate potential of a gaseous discharge tube that has been rendered conducting at the beginning of an interval to be measured. There has also been provided a means to so connect the input terminals of the discharge tubes that the switch used to close the input circuit so as to cause the iirst tube to become conducting may be one that can be either opened or closed. It is to be understood that the discharge tubes shown are merely for purposes of illustration and may take other forms', and that the uses of the words platef "cathode, or grid are to be broadly construed and not limited to that shown. It is also to be understood that the tubes may be reversed irom the position shown, and the cathodes connected together instead of the plates.

This invention is not limited to the details described and illustrated, but is to be construed upon it may be locked by any suitable means.

This will cause switch 1| to close upon contact |05, switch 12 to close upon contact |86, and.

switch 13 to close upon contact |01, and will allow switch J4 to remain open. In order to obt tain the steady state current readings, it is necessary to ascertain the value of the current I flowing through the galvanometer. The tube 56 is started by any desired means. The circuit may be traced from cathode 65, line 85, switch lever 1|, contact |05, resistance 11 (equivalent to resistance of galvanometerl, line |08, line |09, milliammeter 81, line 88, battery 66, line 90, resistance 8|, line 9|, line 92, plate 93. As the resistance 11 is the equivalent of the galvanometer 64, the milliammeter 81 will give a reading of the current which will flow through the circuit when tube 56 becomes conducting.

In order to determine the deflection constant of the galvanometer, it is necessary to charge condenser 18 and then to discharge condenser 18 through the galvanometer so that a reading thereof may be obtained. The switch ||0 is closed and the condenser' 18 will be charged from battery 66 by a circuit that may be traced .75

as covering all equivalent devices falling within the scope of the appended claims.

What is claimed is:

1. In an impulse responsive device, the combination of two normally non-conducting gaseous l discharge tubes, each tube including a plate,

cathode and control grid; a plate-cathode circuit for the rst of said tubes, said circuit including the plate and cathode f the ilrst tube, a source of energy, a resistance and a ballistic galvanorneter directly in said circuit; a platecathode circuit for the second tube including the plate and cathode of the second tube, a second source of energy and said resistance: means to normally bias the control grids of said tubes to maintain the tubes in non-conducting condition; means to impress an impulse on the ilrst control grid to render the tube conducting, thereby causing a flow of current through the ballistic galvanometer; means to impress an impulse on the control grid of the second tube to render the same'conductlng, the additional ilow of current through the resistance from the plate-cathode circuit of the second tube depressing the plate potential of the iirst tube to render the same again non-conducting.

2. In -an impulse responsive device, the combination of two normally non-conducting gaseous discharge tubes, each tube including a plate,

cathode and control grid; a plate-cathode circuit :or uis-am or seid tubes Said circuit including Vthe plate and cathode of the first tube, a source of energy, a resistance and a ballistic galvanometer in series; a plate-cathode circuit for the second tube including the plate and cathode oi the second tube, a'battery and said rst resistance; means to normally bias the control grids of said tubes to maintain the tubes in non-conducting condition; means to impress an impulse on the rst control grid to render the'tube conducting; means to impress an impulse on the control grid o! the second tube to render the same conducting and to cause said battery current to now through said resistance in addition to the first tube flow and thereby depress the plate potential of the first tube to render the same again non-conducting. i

3. In an impulse responsive means, a normally non-conducting gaseous .discharge tube, including a plate. cathode, control grid and a platecathode circuit including said plate and cathode, and a source of energy; means to bias the control grid relative to ground comprising a biasing source of energy connectedl between said grid and ground to maintain the tube normally nonconducting; means for changing the bias to render the tube conducting. said means comprising 'a circuit including a source of energy and a switch connected between said grid and ground in parallel with the rst circuit; and a switch responsive to an impulse connected between said grid and ground so that with the first mentioned switch Open. a closing movement of the second' mentioned switch will change the potential on the grid, and with the iirst mentioned switch closed, an openingmovement of the second mentioned switch will change grid.

4. In van impulse responsive device, the combination comprising two normally non-cominciing gaseous discharge tubes, each tube having a plate, cathode and control grid; means to normail! bias the control grids of said tubes below that required for conduction; means to change thebiasontheiirsttuberesponsivetoanimthe potential on the pulse to render it conducting; means change the bias on the second tube responsive to a second impulse to render the same conducting; a plate-cathode circuit for the first tube including its plate. cathode and a source of energy; a plate-cathode circuit for the second tube including its plate and energy; means in the second plate-cathode circuit connected to the first plate-cathode circuit to depress the plate potential of the first tube below that required for conduction when current flows through the second plate-cathode circuit; the source of energy in-the second circuit providing a current flow until positively interrupted to prevent further impulses on the first tube from rendering the first tube again conducting; and means to measure the time of current flow in the first plate-cathode circuit.

5. In an impulse responsive device, a normally non-conducting gaseous discharge tube including a-plate, cathode, control grid, and a plate-cath- Y ode circuit including said plate and cathode and a source oi energy; input terminals for the device, one of said terminals-being connected to' said control grid by a grid input lead through a condenser having a leak-oft resistance in parallel therewith; means to bias the control grid relative to ground comprising a second circuit including la biasing source of energy connected between said grid and ground to maintain the tube normally non-conducting; means for changing the bias torender the tubeV conducting compris-l ing a third circuit including a source of energy and a switch connected between said grid and ground in parallel with said second circuit, said condenser being located in the grid input lead between said second and third circuits; and a switch responsive to an impulse connected between said 'grid and ground. so that with the Y nrstl mentioned switch open, a closing movement oi the second mentioned switch will change the potential on the grid, andl with the first mentioned switch closed, an opening movement ci the second mentioned switch will change the potential on the grid.

@OUIN IRVING BRADFORD. e PAUL E. LOWE.

cathode, and a som-ce of 

